1. Field of the Invention
The present invention relates to a dielectric ceramic composition and to a dielectric resonator, and, more particularly, to a dielectric ceramic composition which, when employed in a high-frequency setting, exhibits a high unloaded quality factor (Qu) and permits regulation or variation of the relative dielectric constant (εr) and the temperature coefficient (τf) of resonance frequency (fo) within specific ranges in accordance with the particular use or application of the composition. The invention also relates to a dielectric resonator comprising a resonator main body formed from the composition.
2. Description of the Related Art
Some conventional dielectric ceramic compositions are known to be useful in devices operating in high-frequency regions such as the microwave region. Such compositions are suitable for use in a variety of products including dielectric resonators, dielectric antennas, dielectric waveguides, dielectric substrates for microwave integrated circuits (MICs), and multi-layer ceramic capacitors.
In order to be employed in high-frequency operating regions such dielectric ceramic compositions must satisfy the following three basic requirements in accordance with the use or application thereof: (1) the unloaded quality factor (Qu) must be high; (2) the relative dielectric constant (εr) must be large and still must be capable of being regulated or varied over a range of values; and (3) the absolute value of the temperature coefficient (τf) of the resonance frequency (fo) of the composition must be small, and this temperature coefficient must be capable of being regulated or varied over a small range.
Previously proposed dielectric ceramic compositions for use in high-frequency operating regions include a dielectric ceramic composition containing Ba, Nb, Sb, and O2 (Japanese Patent Application Laid-Open (kokai) No. 62-190608), and a dielectric ceramic composition containing Ba, Zn, Ta, and K (Japanese Patent Application Laid-Open (kokai) No. 11-71173).
Although such conventional dielectric ceramic compositions have a relatively high unloaded quality factor (Qu), there are difficulties with the composition in varying or regulating the relative dielectric constant (εr) and the temperature coefficient (τf) of the resonance frequency (fo) thereof, in use of the composition in, for example, a dielectric resonator, a dielectric antenna, a dielectric waveguide, a dielectric substrate for a microwave integrated circuit (MIC), or a multi-layer ceramic capacitor. Therefore, when the dielectric ceramic composition is produced, an appropriate metallic component must be selected based on the specific use of the composition and as a consequence, production of the dielectric ceramic composition is an intricate process.